There are numerous ways to modify DOD contracts. Six basic procedures, termed instruments, are catagorized for the purposes of determining which contract modification instrument was preferred by the various DOD procurement agencies, and which contract modification instrument was considered the most efficient in terms of flexibility, manageability, cost effectiveness, and timeliness. Data for the research were gathered from experienced DOD personnel from the procurement career field. Additionally, the survey data were validated by examining official DOD contract files. While there were distinct preferences among the various DOD agencies, computer analysis of the data revealed that the bilateral supplemental agreement issued under the authority of the Changes clause was the overall most preferred instrument to be used. Through the use of the Friedman Two-Way Analysis of Variance by Ranks Test and the Kendall Coefficient of Concordance Test, it was concluded that the bilateral supplemental agreement issued under the authority of the Changes clause was the most efficient contract modification instrument DOD-wide.